The key to a memorable love story is not just the chemistry between the stars but the acuity of the script in dramatizing exactly what draws two people to each other. Many movies depend on swooning glances but never get beyond clichés in elucidating the bond between the lovers. The love stories that endure — from Gone With the Wind to The Way We Were -- show you why two particular people are made for each other. The low-budget gay British film, Weekend, may not be in a league with those classics, but it has that crucial dramatic spark. The movie is playing at Outfest and other festivals and will be released by IFC’s Sundance Selects in the fall; it should draw strong reviews and even moderate box office, provided that gay audiences will turn out for substance as well as skin.

When Russell (Tom Cullen) meets Glen (Chris New) at a bar on Friday night, a casual sexual fling gradually deepens over the course of the weekend they spend together. Russell is more masculine and somewhat more repressed, like Heath Ledger’s character in Brokeback Mountain. Glen, a younger artist, is more of a provocateur, and he immediately challenges Russell with probing questions about his comfort with his own sexuality. Russell finds himself stimulated by Glen’s directness, and Russell begins to let down his guard, only to learn that Glen is planning to leave on Sunday afternoon for a two-year stay in America. So the film builds toward a poignant parting at the local train station, as the two men realize that their brief encounter has changed both of them profoundly.

The scene that dramatizes Russell’s transformation takes place right before that train station farewell, when Russell opens up for the first time to his straight pal, Jamie (Jonathan Race). Jamie knows that Russell is gay, but Russell has never shared any details of his personal life. Under Jamie’s prodding, Russell confesses his growing love for the man who’s about to leave the country, and his newfound openness convinces us of the subtle but significant influence that Glen has had on him.

The two leading actors give deft, expressive performances that have us rooting for both of them. Cullen has a broodingly sensual presence, while the impish New makes a charmingly prickly foil. One teases and provokes while the other resists and only gradually surrenders emotionally. Director Andrew Haigh (a former editor who worked on several Ridley Scott films) brings a lot of tension to the intimate encounters and makes striking use of the Midlands locations that were also seen 50 years ago in Albert Finney’s breakthrough film, Saturday Night and Sunday Morning.

The film’s frank sex scenes may keep it from crossing over to straight audiences who might otherwise appreciate the insights into the push-and-pull of all romantic relationships. More disturbing is the pair’s hunger for booze and drugs. They consume so much alcohol, pot, and cocaine that it’s sometimes hard to believe they could stay alert enough to sustain a conversation. While Haigh obviously wanted to deglamorize the romance, he sometimes plunges too far into the funk. The script and the performances, however, overcome the sordid details.